The present invention relates to machines for depositing a liquid or viscous fluid to moving surfaces, in particular by means of impression or deposition cylinders being fed with fluid by means of a screen transfer cylinder cooperating with a scraper chamber, the objective being an end sealing system for such scraper chamber.
In general, the scraper chambers of printers or machines applying a viscous or liquid product consist of a longitudinal recess running over the full width and opposite a screened transfer cylinder and are fitted with feed means for a viscous or liquid fluid and further with means to deposit this fluid by aspiration onto the surface of the cylinder. These chambers include longitudinal scrapers running along generatrices of the transfer cylinder and serving, on one hand, to preclude the fluid from leaking out of the chamber and on the other hand to implement accurate application of the fluid volume as defined by the volume of the cylinder alveoles. In general, these scrapers are steel or plastic blades resting against the screen surface of the transfer cylinder.
The scraper chambers are fitted at their ends with a sealing system which may be a single or multiple seal resting against the corresponding ends of the screen transfer cylinder. This sealing system also applies the scrapers against the screen transfer cylinder by acting on their ends and by imparting to them a movement toward the screen cylinder.
More or less effective sealing systems are known in the state of the art, however they entail rapid scraper wear.
It is known, for example, to use a silicone seal mounted at the end of the scraper chamber and which closely follows its contour as well as that of the screen cylinder. This seal is forced against the end edges of the scraper chamber, against the scraper surface on the side opposite the screen cylinder, and against the corresponding end surface of the screen cylinder. However, such a sealing system allows sealing only for a short time because of being subjected to rapid wear caused by friction with the screen cylinder. Accordingly, this seal must be replaced frequently at corresponding machine shutdown and has corresponding loss in efficiency.
French patent application 2,687,096 describes a sealing system consisting of a set of parts. Such sealing system improves sealing at the ends of the scraper chamber because the parts resting against the end of the screen cylinder are subject to a more or less constant pressure easing wear. However, because these pressurized parts simultaneously force the corresponding ends of the steel or plastic scrapers against the screen cylinder, fairly rapid wear of scrapers and seals entails premature replacement.
Lastly, German patent application 4,241,792 discloses a scraper-chamber end sealing system consisting of a number of parts implementing a labyrinth seal to collect the fluid trying to escape at the ends of the screen cylinder. This seal is mounted between two adjoining alveolar elements pressed against a corresponding circumferential strip of the screen cylinder. The assembly so formed constitutes a sealing system elastically pressed against the corresponding end of the screen cylinder.
However, due to the labyrinth seal being made of an alveolar substance without compensating for losses in elasticity due to material fatigue, the sealing ability of this device soon becomes problematical because this labyrinth no longer is being sufficiently compressed. Moreover, because the scraper ends are forced against the screen cylinder solely by the pressure from the alveolar elements, their sealing ability suffers from the same problems as the labyrinth seal.
The objective of the present invention is to palliate these drawbacks by proposing an end sealing system for a scraper chamber of a printer or a machine depositing a viscous or liquid fluid on a surface, the sealing system ensuring constant sealing ability over an extended time at the ends of the screen transfer cylinder and of the scraper chamber while nevertheless avoiding premature cylinder wear, in particular in the case of mechanically engraved cylinders which then are chrome-plated, and/or scrapers, as well as sealing elements.
For that purpose, the end sealing system for a scraper chamber of a printing machine or a machine depositing a viscous or liquid fluid on a surface, where the chamber cooperates with the screen transfer cylinder, is characterized in that it includes a mounting frame housed at the end of the scraper chamber, an elongated seal made of a deforming alveolar material and cooperating at its ends with the mounting frame, and a rigid, second seal mounted on the elongated seal between the ends of the latter and guided in the mounting frame, the ends of the elongated seal resting underneath the scraper ends on the side opposite the screen transfer cylinder.